Disease

[CHLE_HUMAN] Defects in BCHE are the cause of butyrylcholinesterase deficiency (BChE deficiency) [MIM:177400]. BChE deficiency is a metabolic disorder characterized by prolonged apnoea after the use of certain anesthetic drugs, including the muscle relaxants succinylcholine or mivacurium and other ester local anesthetics. The duration of the prolonged apnoea varies significantly depending on the extent of the enzyme deficiency. BChE deficiency is a multifactorial disorder. The hereditary condition is transmitted as an autosomal recessive trait.

Function

[CHLE_HUMAN] Esterase with broad substrate specificity. Contributes to the inactivation of the neurotransmitter acetylcholine. Can degrade neurotoxic organophosphate esters.[1][2]

Publication Abstract from PubMed

Organophosphylates (OPs) exert their acute toxicity through inhibition of acetylcholinesterase, by phosphylation of the catalytic serine. Engineering of human butyrylcholinesterase by substitution of histidine for glycine at position 117 led to the creation of OP hydrolase activity. But the lack of structural information and poor understanding of the hydrolytic mechanism of G117H has hampered further improvements in the catalytic activity. We solved the crystallographic structure of the G117H mutant with a variety of ligands in the active site. A sulfate anion bound to the active site suggested the positioning for an OP prior to phosphylation. A fluoride anion was found in the active site when NaF was added to the crystallization buffer. In the fluoride complex, the imidazole ring from His117 was substantially shifted adopting a relaxed conformation most likely close to that of the unliganded mutant enzyme. Additional X-ray structures were obtained from the transient covalent adducts formed upon reaction of G117H with the OPs echothiophate and VX. The position of His117 shifted in response to the introduction of these adducts, overlaying the phosphylserine. These structural data suggest that the dephosphylation mechanism involves either a substantial conformational change of His117 or an adjacent nucleophilic substitution by water.